1. Field of the Invention
The present invention relates to the xerographic printing art, and more particularly to a method and apparatus for printing a composite record based on or derived from first and second complementary sources of information.
2. Description of the Prior Art
In the most common form of xerographic printing process, a document or record is imaged onto a photoconductor to which has been applied a uniform electrostatic charge. The incidence of the light pattern on the photoconductor causes those areas subjected to light energy to become electrically conductive and allow for the passage of charge to ground; those areas of the photoconductor not exposed to light energy remain electrically insulative and retain their electrostatic charge distribution. The net effect of the imaging process is to create a latent electrostatic image of the document or record. This electrostatic image may then be developed by the application of toner material. The developed image can then be transferred from the photoconductive surface onto a record medium.
The xerographic printing process just described is regarded as a simple positive-to-positive transfer of an original document. More specifically, black areas on the original document will be represented by an electrostatic charge pattern, and white areas will be represented by the absence of electrostatic charge. Stated otherwise, the absence of light in an image pattern represents information, and the presence of light represents non-information or is without informational significance. This relationship is well suited to a xerographic reproduction process for the copying of an original document. Positive printing can be reversed by use of a negative original but this usually requires a secondary process to make the negative original.
Moreover, the information to be xerographically printed may take an alternative embodiment other than an original document. For example, the information may be imaged by means of a scanning laser whose output is modulated in accordance with the flow of information. This particular embodiment is well adapted to interface a digital computer with a xerographic printer. In these instances, a latent electrostatic image may be formed in the negative mode to accommodate the laser, i.e. the presence of light will now signify information, and the absence of light will signify the absence of information. The formation and processing of negative latent electrostatic images is known in the art and is not novel in itself.
However, one can envision a system where it is advantageous to have the capability to xerographically print, both individually or jointly, information derived from an original positive document and information derived from a second source, such as a central processing unit interfacing to the xerographic printer through a negative mode laser. A printer system incorporating both of these features must make accommodation for the inherently conflicting characteristics of printing from an original positive document combined with printing from a negative mode laser output. Put more specifically, printing from an original positive document connotes a positive mode electrostatic image; and printing from a scanning light source such as a laser connotes a negative mode electrostatic image.
A good example of where one may want to combine the xerographic reproduction of an original document with the xerographic printing of computer generated data is in an accounting environment where periodically reports of several various accounts must be generated. Each account report may contain recurring information that may be regarded as fixed data, together with specific non-recurring information peculiar to that individual account that may be regarded as variable data. A practical example would be a monthly statement prepared by a bank and sent out to its savings account customers. The heading and format information would represent the fixed data, and the account information containing the depositor's name, account number, dates and amounts of transactions, etc. would represent the variable data. A xerographic printing system containing the capability to print a composite record containing both the fixed and variable data would be very advantageous in this environment.
It is the principal objective of the present invention to provide a xerographic copying system that incorporates the capability of printing both fixed positive image data along with variable data onto a single composite record.